This invention relates to an optical disc including guide grooves and pits, and more particularly to improvements for obtaining reasonable push-pull signals.
Optical discs using the so-called ISO standard have spiral guide grooves, wherein emboss shaped pits are molded (formed) in advance between respective grooves at the inner circumferential portion or the header portion.
In such optical discs, the optical pick-up is subjected to seek operation in the radial direction of the disc to move it to the target track on the basis of tracking error signal (so called push-pull signal) from the groove. In that regard, a threshold is set in the vicinity of center value of the push-pull signal to detect how many times the push-pull signal crosses (traverses) this threshold to thereby count the number of tracks to detect the target track. At the same time, the target address is detected on the basis of an address signal from the emboss shaped pit to carry out recording or reproduction of information.
Meanwhile, in these optical discs where pits in emboss form are molded in advance between respective as described above, a phenomenon occurs in that the signal amplitude of the tracking error signal (the so called push-pull signal) in the area including pits is reduced to one half (1/2).about.one third (1/3) as compared to the signal amplitude in the area comprised of only grooves.
This is because an approach has been conventionally preferentially employed to take the information signal amplitude from the area comprised of only grooves as a large value, so the tracking error signal from the area including pits is sacrificed.
Accordingly, when the tracking error signal is greatly reduced in the area including pits by the phenomenon described above, inconveniences occur such that tracking cannot be precisely under taken and/or any error takes place in the tracking count operation.